How a Photoacoustic CO2 Sensor Works

The concentration of carbon dioxide in indoor air can affect people's health and comfort. When indoor air does not circulate, the concentration of carbon dioxide will rise, causing people to feel drowsy, headaches, lack of concentration and other symptoms. Therefore, real-time detection and regulation of indoor carbon dioxide concentration is an important measure to improve the quality of life and work efficiency. This article will introduce a carbon dioxide sensor based on photoacoustic sensing technology, which has the characteristics of small size, low cost, high accuracy, etc., and can meet the needs of various portable detection equipment.

The effect of CO2 concentration on the human body

What is photoacoustic sensing technology?

Photoacoustic sensing technology is a technique that uses the interaction of light and sound waves to detect the concentration of gas. Its basic principle is: in a specially designed cavity, an infrared light source periodically emits infrared light of a certain wavelength range, which can be absorbed by the target gas molecules (such as carbon dioxide), causing the gas sample to heat up and cool down rapidly in the cavity. This temperature change leads to the pressure change of the gas, which in turn generates sound wave signals. By using a miniature microphone to receive these sound wave signals, and performing signal processing and analysis, the concentration value of the target gas can be obtained. Since different kinds of gas molecules have different absorption characteristics for different wavelengths of infrared light, it is possible to select the appropriate infrared light source and filter to achieve the detection of specific gas.

Schematic of a typical Photoacoustic sensor

The advantages of photoacoustic carbon dioxide sensors

Compared with the common infrared absorption method (NDIR) based carbon dioxide sensors on the market, photoacoustic carbon dioxide sensors have the following advantages:

• Small size: Because photoacoustic sensing technology uses a microphone as the detection element, instead of a large optical cavity to ensure the stability of the optical path like NDIR, photoacoustic carbon dioxide sensors can be very small and light, suitable for portable devices.
• Low cost: Because photoacoustic sensing technology uses low-cost components such as ordinary infrared LEDs and microphones, instead of expensive and high-precision components such as infrared lasers and detectors like NDIR, photoacoustic carbon dioxide sensors can significantly reduce manufacturing costs.
• High accuracy: Because photoacoustic sensing technology uses periodic infrared pulses to excite the target gas, instead of continuous infrared beams to detect the target gas like NDIR, photoacoustic carbon dioxide sensors can avoid signal attenuation and errors caused by factors such as light source aging, optical path offset, environmental temperature change, etc., thereby ensuring the accuracy and stability of the measurement.

NDIR vs Photoacoustic

Product Recommendation

DFRobot offers a small-sized photoacoustic carbon dioxide sensor. Its measurement range is 400 - 5000 ppm, and the accuracy is ±(40 ppm + 5% MV). It has an I2C interface, which can be easily connected to microcontrollers such as Arduino.

If you want to know more about this sensor, you can click here to view and purchase.

To demonstrate how to use this sensor, we made a portable carbon dioxide concentration indicator keychain. It can display the current carbon dioxide concentration, so that we can go outdoors to breathe fresh air or open windows for ventilation in time.

Click here to view the tutorial.